1. FIeld of the Invention
This invention relates broadly to the art of glassmaking. More particularly, it is concerned with a method and apparatus for mixing unmelted batch materials with molten glass in a glass melting tank or furnace in order to improve the melting efficiency of the furnace.
2. Description of the Prior Art
In the manufacture of glass, raw materials are first melted and reacted to form molten glass. This molten glass is then conditioned and formed into useful articles. Raw batch materials for manufacturing glass comprise scrap glass or cullet, sand, limestone, soda ash, salt cake, rouge and the like. Raw batch materials are charged to a glass melting furnace in the continuous manufacture of glass. Heat is supplied within the glass melting furnace to melt the raw batch materials and permit the necessary reaction to occur so that molten glass is formed from batch materials.
Conventionally known glass melting furnaces are generally either recuperative furnaces or regenerative furnaces. These furnaces are provided with means for supplying heat to batch materials and molten glass contained in the furnace by the combustion of fuels using preheated air. Heat is generally supplied to the molten glass and the glass batch materials by burning a fossil fuel such as oil, gas or powdered coal in a space above the molten glass and glass batch materials so that flames pass over them causing a transfer of heat to them. Additional heat may be supplied to the molten glass in such furnaces by using submerged heaters, typically electric heaters. Also furnaces using electric heaters alone have been known.
In typical conventional furnaces, a chamber for containing the molten glass is provided. The chamber for containing glass comprises the bottom of the furnace, side walls which are generally parallel to the general movement of glass through the furnace, a back wall in the vicinity of which raw batch materials are fed or charged into the furnace and a front wall at the opposite end of the furnace from the back wall in the vicinity of which conditioned molten glass is removed from the furnace for forming. Extending over the chamber of the furnace is a roof which provides a headspace above the molten glass. The heating flames are directed into this headspace above the molten glass, generally from firing ports located along the opposing side walls of the furnace.
Raw glass batch materials are charged to the furnace generally through an opening in its back wall. Most conventional furnaces are provided with a "fill doghouse" extending outwardly a short distance from the back wall. Raw glass batch materials are charged into the furnace through such a fill doghouse. They may be charged continuously using a blanket feeder or the type described in the following U.S. Pats. Nos. 1,623,057 and 2,624,475 which show devices for feeding a single layer of batch; U.S. Pat. Nos. 2,114,545 and 2,711,837 which show continuous belt devices for feeding two layers -- one of cullet and one of batch over the cullet; U.S. Pat. No. 2,829,784 which shows a rotating paddle device for feeding two layers -- one of cullet and one of batch; and U.S. Pat. No. 2,773,611 which shows a device for feeding three layers of batch and cullet.
Alternatively, glass batch materials may be charged using intermittent push feeders such as described in the following U.S. Pats. Nos. 1,483,278, 1,913,665, 1,916,262, 1,917,247, 1,953,221, 2,281,050, 2,284,398, 2,284,420, 2,471,336, 2,556,467, 2,815,135 and 3,193,119 which show devices for feeding continuous transverse logs of batch; U.S. Pat. No. 2,831,567 which shows side wall pushers; U.S. Pat. No. 2,934,221 which shows a device for feeding divided logs and U.S. Pat. No. 509,930, U.S. Pat. Nos. 1,928,016 and 1,941,897 which show devices for feeding two or more streams of batch intermittently to a furnace.
However, the glass batch materials enter the furnace; following charging, they float along the surface of molten glass contained within the bottom portion of the furnace as a blanket-like layer. The blanket-like layer of raw batch material advances along the surface of molten glass in the glass melting furnace in a downstream direction away from the fill doghouse and toward the front wall of the furnace. As the blanket-like layer of glass batch materials float downstream through the glass melting furnace, it receives heat both from the heating flames extending over it and from the molten glass beneath it. This causes the batch materials to melt and react forming more molten glass. Usually, but not always, a blanket-like layer of raw batch materials in the vicinity of the fill doghouse is substantially continuous and extends nearly from one side wall to the opposite side wall of the furnace. As the batch materials move through the glass melting furnace, melting occurs and the blanket of batch material gradually breaks up into individual floating islands or logs of batch material. In a conventional, regenerative furnace having six or seven firing ports on each side and producing glass at a rate of 400 to 500 tons per day, the floating glass batch is found to melt out by about the third to fourth firing port downstream from the fill doghouse. Downstream of the location where the floating batch material is melted out, there extends for a short distance a surface foam on the surface of the molten glass as volatile products of reaction are refined from the molten glass.
The blanket-like layer of unmelted glass batch materials, which floats along the surface of the pool of molten glass, acts as a thermal insulator so that glass batch materials inside the blanket do not readily recieve sufficient heat for rapid melting and reaction either from the molten glass beneath the blanket of batch or from the flames above the blanket of batch. Workers in the art of glassmaking have developed a variety of techniques for enhancing the melting of glass batch materials. For example, U.S. Pat. No. 2,533,826 to Lyle describes a batch-enfolding device for use in a fill doghouse. A rabble is provided which is moved in an orbital motion so that molten glass is brought up from beneath the floating blanket of glass batch material and folded over portions of batch materials in successive folds. This has the effect of providing better heat transfer between molten glass and the unmelted batch materials but also has the effect of isolating unmelted batch material somewhat from the heating flames above them. If molten glass enfolding is substantially complete, the molten glass over a pocket of unmelted batch serves as a reflector to reflect heat from the flames away from the molten glass and may actually reduce the rate in which the unmelted batch inside the layer of batch reacts and melts.
While the melting enhancement techniques of the past have been primarily directed to acting upon glass batch material in or near the fill doghouse of a glass melting furnace, the unmelted batch advancing downstream through the furnace between the firing port has been largely ignored and permitted to melt at its natural rate in such furnace surroundings. The present invention contemplates a technique for enhancing the melting of glass batch materials in the space of a glass melting furnace where heat is applied to the glass by improving the transfer of heat directly to the advancing glass batch.